I've spent many a happy hour arguing with American home brewers that kettle souring isn't the traditional way to brew Berliner Weisse.
Franke, and his short-lived shortcut method of producing Berliner was only ever employed briefly, before being discarded for one very good reason. Which we'll get to later.
Good old Schönfeld dexcribes the method, as well as its advantages and disadvantages.
"e) Francke acidification process
Making distillery lactic acid bacteria usable for the production of Berlin Weissbier was the effort of O. Francke, who also put the process into practical use for some time. A sour starter is made from a pure culture of Bacillus Delbrücki using unhopped wort and wort, which has been run off from off the lauter tun and cooled down to 45-47ºC, is inoculated with it. Subsequent runnings must also be cooled to this temperature. The acidification takes place quickly and, depending on the circumstances, reaches a lactic acid content of 0.18-0.20% in 5-7 hours, which is enough for the formation of a sufficiently sour taste, but must not be exceeded, as this is associated with the risk that the work of the yeast is damaged both in terms of growth and fermentation ability. To prevent further acidification, the wort must then be heated to 80° C and held for one hour.
When cultivating the sour starter, it is advisable to inoculate 100 ccm of wort in the most vigorous bacterial development with new (5 l) wort, this again after reaching the highest development, which at the required optimum temperature of 45-47° C after the course of 24-28 hours is the case, is transferred to new wort (about 3–5 hl), which, with sufficient development after 24 hours, can now serve as sour starter for acidifying a brew of 30–50 hl. Inoculation material can always be removed from the sour starter for the creation of new sour starters. If the brewing does not take place continuously, but only sporadically after longer intervals, it becomes necessary to put the removed inoculum in a cold place in order to keep the lactic acid bacteria viable."
"Obergärige Biere und ihre Herstellung" by Dr. Franz Schönfeld, 2nd edition, Verlag von Paul Parey, Berlin, 1938, page 155.
Basically, you run off some unhopped wort and throw in your lactobacillus starter. Pretty simple, really. You let it sour for a few hours, then pasteurise it at 80° C. Which is a pretty high temperatue, which will also kill all the lactobacillus stone dead.
That sounds great. Much simpler than the complicated symbiotic fermentation of Saccharomyces and lactobacillus. There was just one hitch:
"Artificial (biological) acidification has the great advantage of protecting Weissbier from any kind of infection by other bacteria through the immunity it generates. It allows the abandonment of the use of the old yeast and to switch to the use of pure yeast and ensuresthe production of a long-life beer that is resistant to lengthening (Langwerden), termobacteria and acetic acid bacteria. However, these advantages did not suffice to outweigh the disadvantages, which are expressed in a shift in properties and which are considered so essential that the use of the biological acidification process, which has been tried in various practical ways, has again been abandoned. After all, the process is suitable for producing a sour and pleasant-tasting beer, even if it does not have the full characteristics of the Berlin Weissbier."
"Obergärige Biere und ihre Herstellung" by Dr. Franz Schönfeld, 2nd edition, Verlag von Paul Parey, Berlin, 1938, page 155-156.
My apologies, nut I've no idea what Langwerden is. Other than it's some sort of bacteria.
What was the problem with Francke's method? Beer produced by it didn't taste like Berliner Weisse. You could produce a pleasantly sourish beer. But without the characteristics of Berliner Weisse.
Why was that? Because it lacked the involvement of Brettanimyces, which wa responsible for an important flavour element.
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